Polyester Elastomer Composition

ABSTRACT

The invention provides a polyester elastomer composition comprising (A) a polyester elastomer, (B) an epoxy compound having at least one epoxy group in the molecule thereof, and (C) a polycarbodiimide compound having at least two carbodiimido groups in the molecule thereof, wherein each of two carbon atoms both adjacent to each carbodiimido group has at least one group among (i) an alkyl group having 1 to 4 carbon atom(s) and (ii) a substituent exhibiting electronic effect of lowering reaction rate, and wherein the amounts of the epoxy compound (B) and the polycarbodiimide compound (C) are 0.01 to 10 parts by weight and 0.01 to 10 parts by weight, respectively, relative to 100 parts by weight of the polyester elastomer (A). The polyester elastomer composition is excellent in terms of hydrolysis resistance, heat resistance, oil resistance, wear resistance, and impact resistance.

TECHNICAL FIELD

The present invention relates to a polyester elastomer compositioncomprising a polyester elastomer, an epoxy compound, and apolycarbodiimide compound. Products obtained by processing the polyesterelastomer composition are excellent in hydrolysis resistance, heatresistance, oil resistance, impact resistance, and wear resistance.

BACKGROUND ART

Polyester elastomers have been suitably employed for producingautomobile parts or other articles, by virtue of their excellentphysical properties such as heat resistance, oil resistance, and impactresistance. Polyester elastomers, however, having poor hydrolysisresistance, readily undergo thermal deterioration during processingthereof. Thus, polyester elastomers have serious problems, includingsudden decrease in strength or impact resistance, variation in meltviscosity during molding, and poor durability for serving as automobileparts.

Conventionally, a variety of countermeasures have been taken so as toimprove hydrolysis resistance of polyester elastomers.

Japanese Patent Application Laid-Open (kokai) No. 58-162654 (see Claims,lower left column to lower right column on page 364, and Examples 1 to5) discloses that a mono-functional epoxy compound and a bi-functionalepoxy compound are added in an amount of 0.3 to 10 wt. % to a polyesterelastomer so as to improve hydrolysis resistance.

Japanese Patent Application Laid-Open (kokai) No. 59-152947 (see Claims,upper left column to lower left column on page 313, and Examples 1 and2) discloses that an epoxy compound having one or more functionalities,a weather stabilizer, and a tertiary phosphine are added to a polyesterelastomer.

Japanese Patent Application Laid-Open (kokai) No. 50-160362 (see Claims,lower right column on p. 364, and Examples 1 and 2) discloses that apolycarbodiimide is added in an amount of 0.1 to 10 parts by weight to apolyester elastomer so as to improve hydrolysis resistance.

Among these approaches for improving hydrolysis resistance of apolyester, an approach including addition of a polycarbodiimide is mostadvantageous. However, a conventionally employed polycarbodiimide hasthe drawback that it reacts with water, leading to a decrease inpolycarbodiimide concentration; i.e., an intrinsic role thereof that itcaptures a protonic acid generated through hydrolysis of ester cannotfully be attained.

Thus, an object of the present invention is to provide, on the basis ofimprovement in hydrolysis resistance, a polyester elastomer compositionhaving excellent heat resistance, oil resistance, wear resistance, andimpact resistance.

DISCLOSURE OF THE INVENTION

The present inventor has carried out extensive studies in order toovercome the drawback residing in conventional techniques, and has foundthat a polyester elastomer composition comprising a polyester elastomer(A) with specific amounts of an epoxy compound (B) and a specificpolycarbodiimide compound (C) exhibiting low reactivity to water hasremarkably enhanced hydrolysis resistance, as compared withconventionally attained hydrolysis resistance. The present invention hasbeen accomplished on the basis of this finding.

Accordingly, a first mode of the present invention provides a polyesterelastomer composition comprising (A) a polyester elastomer, (B) an epoxycompound having at least one epoxy group in the molecule thereof, and(C) a polycarbodiimide compound having at least two carbodiimido groupsin the molecule thereof, wherein each of two carbon atoms both adjacentto each carbodiimido group has at least one group among (i) an alkylgroup having 1 to 4 carbon atom(s) and (ii) a substituent exhibiting anelectronic effect of lowering reaction rate, and wherein the amounts ofthe epoxy compound (B) and the polycarbodiimide compound (C) are 0.01 to10 parts by weight and 0.01 to 10 parts by weight, respectively,relative to 100 parts by weight of the polyester elastomer (A).

A second mode of the present invention is drawn to a specific embodimentof the polyester elastomer composition of the first mode, wherein thepolyester elastomer (A) contains a crystalline aromatic polyester as ahard segment and at least one species selected from the group consistingof an aliphatic polyester, an aliphatic polyether, and an aliphaticpolycarbonate as a soft segment.

A third mode of the present invention is drawn to a specific embodimentof the polyester elastomer composition of the second mode, wherein thealiphatic polyester as the soft segment comprises a polycaprolactonecomponent.

A fourth mode of the present invention is drawn to a specific embodimentof the polyester elastomer composition of the first mode, wherein thepolycarbodiimide compound (C) is a compound represented by the followingformula:

wherein R represents a hydrogen atom, an alkyl group having 1 to 4carbon atom(s), or a substituent exhibiting an electronic effect oflowering reaction rate; two Rs linking to a certain carbon atom may bethe same or different from each other, provided that the two Rs are notcoincidentally hydrogen atoms; n is an integer of not less than 2.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will next be described.

Polyester Elastomer (A)

The polyester elastomer (A) employed in the present invention containsan aromatic polyester as a hard segment and at least one speciesselected from the group consisting of an aliphatic polyester, analiphatic polyether, and an aliphatic polycarbonate as a soft segment.

No particular limitation is imposed on the mode of linkage of hardsegments and soft segments, and examples of the mode may include acomplete block in which an end of a hard segment is linked to an end ofa soft segment; a block-random in which an end of a block is linked to arandom portion; a random block in which block portions are present in amolecular chain at random; and a mixture thereof.

The aromatic polyester as the aforementioned hard segment has a meltingpoint of 200 to 300° C., and preferably 210 to 280° C. Examples of thepolyester may include a polybutylene terephthalate, a polyethyleneterephthalate, a polyethylene naphthalate, and a mixture thereof. Theremay also be employed an analogous polyester where a portion ofterephthalate is substituted by isophthalate and copolymer polyestersformed from p-hydroxybenzoic acid, 6-hydroxy-2-carboxynaphthalene, or asimilar comonomer, so long as these polymers have a melting pointfalling within the above range.

The aforementioned soft segment has a melting point of 170° C. or lower.Preferably, the soft segment exhibits no clear melting point.

Typical examples of the aliphatic polyester as the aforementioned softsegment may include polylactones, condensates of an aliphatic dibasicacid and an aliphatic glycol, condensates of an aliphatichydroxyalkylcarboxylic acid, and condensates of a mixture thereof.

Examples of monomers for forming the polylactones may includeε-caprolactone, methylated ε-caprolactone, β-propiolactone,γ-butyrolactone, δ-valerolactone, and enantholactone. The polylactonesmay have the form of a homopolymer, a copolymer of two or more monomers,and a mixture of homopolymers, and a mixture of copolymers.

The polylactones may be produced through ring-opening polymerization ofthe aforementioned monomers in the presence of a mono-functional orpolyfunctional initiator. Alternatively, the polylactones may beproduced through condensation polymerization of the correspondinghydroxyalkylcarboxylic acid.

Examples of the aliphatic polyester may include polycaprolactones,caprolactone copolymers, polylactic acid-based or polyglycolicacid-based copolymers, condensates of a glycol such as ethylene glycol,1,4-butanediol, or neopentyl glycol with adipic acid, and condensates ofthe above glycol with sebacic acid or succinic acid. Examples alsoincludes co-condensates thereof and co-condensates with an aromaticpolyester resin in an amount of not more than 30 wt. %.

Among aliphatic polyesters, polycaprolactones and adipic acid-derivedpolyesters are generally employed. However, the polycaprolactones arepreferred from the viewpoint of heat resistance, durability, andflexibility.

The aliphatic polyether as the aforementioned soft segment is a polymerof a cyclic ether or a condensate of a glycol, and also includes acopolymer thereof with caprolactone. Concrete examples of the polyethermay include a polytetramethylene glycol (a polytetramethylene etherglycol), a polyethylene glycol, and a polypropylene glycol. Of these, apolytetramethylene glycol is preferably employed.

The aliphatic polycarbonate as the aforementioned soft segment is apolymer of a cyclic carbonate or a condensate of a polyhydric phenoland/or glycol with phosgene or diphenyl carbonate and the like, andincludes a copolymer thereof with caprolactone. Examples of thealiphatic polycarbonate may include a poly(dimethyltrimethylenecarbonate), a poly(monomethyltrimethylene carbonate), apoly(trimethylene carbonate), and a poly(hexamethylene carbonate).

Regarding the ratio of the hard segment relative to the soft segment inthe polyester elastomer (A) employed in the present invention, thepolyester elastomer (A) has a hard segment content of 50 to 90 wt. %,and preferably 60 to 80 wt. %. When the hard segment content is lessthan 50 wt. %, heat resistance and oil resistance decrease, whereas whenthe hard segment content is in excess of 90 wt. %, impact resistancedecreases. Needless to say, both cases are not preferred.

Incidentally, the sum of the hard segment content and the soft segmentcontent is 100 wt. %. In the case where an aromatic polyester resin iscopolymerized in an amount of not more than 30 wt. % in the softsegment, if the aromatic polyester resin has a melting point of 200 to300° C., the incorporated aromatic polyester content is counted as partof the hard segment content.

The molecular weight of the polyester elastomer (A) may be determinedthrough intrinsic viscosity measurement or GPC. Routine GPC measurementis conducted by use of chloroform/hexafluoroisopropanol=9/1 (vol.) as asolvent and is reduced to standard polystyrene. The polyester elastomer(A) preferably has a molecular weight of 40,000 to 200,000, and morepreferably 40,000 to 150,000, from the viewpoint of well balanced impactresistance and moldability.

Epoxy Compound (B)

No particular limitation is imposed on the epoxy compound (B) employedin the present invention, so long as the compound has at least one epoxygroup in the molecule thereof.

Examples of the epoxy compound (B) may include bisphenol type epoxycompounds produced through reaction of bisphenol A, bisphenol F and soon with epichlorohydrin; novolak type epoxy compounds produced from anovolak resin and epichlorohydrin; glycidyl esters produced from analiphatic or aromatic carboxylic acid and epichlorohydrin; alicycliccompound-derived epoxy compounds produced from an aliphatic compoundhaving a hydroxyl group or a carboxyl group; glycidyl ethers producedfrom epichlorohydrin and an aliphatic or aromatic compound having analcoholic hydroxyl group; epoxidized butadiene; and epoxy compoundsproduced from compounds having a double bond and a peroxide. Specificexamples include methyl glycidyl ether, phenyl glycidyl ether,diethyleneglycol diglycidyl ether, phthalic acid diglycidyl ester,terephthalic acid diglycidyl ester, hexahydrophthalic acid diglycidylester, 3,4-epoxycyclohexylmethanol 3,4-epoxycyclohexanecarboxylic acidester, an epoxidized polybutadiene, and an epoxidizedstyrene-butadiene-styrene block copolymer (epoxidized SBS).

Of these, epoxy compounds having not less than two epoxy groups arepreferred.

The epoxy compound (B) serves as a hydrolysis inhibitor.

Polycarbodiimide Compound (C)

The polycarbodiimide compound (C) employed in the present invention hasat least two carbodiimido groups in the molecule thereof. In thecompound, each of two carbon atoms both adjacent to each carbodiimidogroup has at least one group among (i) a methyl or more bulkysubstituent (i.e., an alkyl group having 1 to 4 carbon atom(s)) and (ii)a substituent exhibiting electronic effect of lowering reaction rate.Examples of the substituent exhibiting effect of lowering reaction rateof the carbodiimido group with water may include alkoxy groups such asmethoxy and ethoxy; halogen atoms such as chlorine and fluorine;haloalkyl groups such as chloroalkyl groups and fluoroalkyl groups; anitro group; an amino group; a carboxyl group; a sulfo group (—SO₃—); acyano group; an aryl group; an acyl group and so on. Thepolycarbodiimide compound (C) may be, for example, produced throughheating and decarbonation of a diisocyanate compound serving as astarting material.

Concrete examples of the polycarbodiimide compound (C) may includecompounds represented by the following formula:

wherein R represents a hydrogen atom, an alkyl group having 1 to 4carbon atom(s), or a substituent exhibiting an electronic effect oflowering reaction rate; two Rs linking to a certain carbon atom may bethe same or different from each other, provided that the two Rs are notcoincidentally hydrogen atoms; R is preferably a methyl group; n is aninteger of not less than 2, preferably not less than 4; the compound (C)may be a mixture of species having different condensation degrees; anaromatic ring may be entirely or partially hydrogenated by hydrogen; andno particular limitation is imposed on the relative position between twocarbodiimido groups or between a carbodiimido group and an NCO groupwhich serve as substituent on an aromatic ring, with an meta- or apara-position being preferred).

The polycarbodiimide compound (C), which prevents a carbodiimide groupthereof from reaction with water, selectively captures a protonic acidgenerated in a system of the elastomer composition when the compositionis in contact with water or is processed.

Preferably, the polycarbodimiide compound (C) has not less than fourcarbodiimido groups in the molecule thereof and a molecular weight(number average) of not less than 500, more preferably not less than1,000, from the viewpoint of hydrolysis resistance. The polycarbodiimidecompound (C) has a carbodiimido group content of not less than 3 wt. %,and preferably 5 to 17 wt. %.

Polyester Elastomer Composition

The polyester elastomer composition of the present invention comprises apolyester elastomer (A) in an amount of 100 parts by weight; an epoxycompound (B) in an amount of 0.01 to 10 parts by weight; and apolycarbodiimide compound (C) in an amount of 0.01 to 10 parts byweight. Preferably, the composition contains an epoxy compound (B) in anamount of 0.1 to 5 parts by weight and a polycarbodiimide compound (C)in an amount of 0.1 to 4 parts by weight. More preferably, thecomposition contains an epoxy compound (B) in an amount of 0.1 to 3parts by weight and a polycarbodiimide compound (C) in an amount of 0.5to 3 parts by weight.

When the epoxy compound (B) content or polycarbodiimide compound (C)content is in excess of the upper limit of the above range, moldedproducts obtained from the polyester elastomer composition have reducedheat resistance, oil resistance, wear resistance, rigidity, and otherproperties, whereas when the content is excessively small, improvementof hydrolysis resistance cannot fully be attained. Both cases are notpreferred.

Since the polyester elastomer composition of the present inventioncontains an epoxy compound (B) and a specific polycarbodiimide compound(C) in combination, hydrolysis resistance of a polyester elastomer canbe suppressed, thereby minimizing thermal deterioration duringprocessing of the composition.

The polyester elastomer composition of the present invention may beproduced through a known means. For example, predetermined amounts ofcomponents are preliminary mixed by use of a mixer such as a Henschelmixer, a tumble blender, or a kneader, followed by kneaded with anextruder, or melt-kneaded with a heating roller or a Bunbury mixer, andpelletized or pulverized.

A variety of additives may be added in accordance with needs to thecomposition of the present invention, so long as the effects of thepresent invention are not impaired. Examples of the additives mayinclude fillers, lubricants, reinforcing agents, stabilizers,weather-stabilizers, UV-absorbers, plasticizers, anti-static agents, andhue-improvers.

Processed products obtained from the polyester elastomer composition ofthe present invention are excellent in terms of heat resistance, oilresistance, wear resistance, impact resistance, and hydrolysisresistance. The polyester elastomer composition of the present inventionmay be used singly or in combination with another resin. Alternatively,the composition of the present invention may be laminated with anothermaterial.

The composition of the invention is employed as automobile parts, largemachine parts, industrial machine parts, domestic electric articleparts, etc. Examples of processed products include hoses, tubes, belts,gears, connectors, tanks, battery parts, sockets, wire coatings, bumpersand so on.

EXAMPLES

The present invention will next be described in more detail by way ofexamples, which should not be construed as limiting the inventionthereto.

[Method of Evaluation]

50% Modulus: JIS K 7113

Tensile strength at break: JIS K 7113

Tensile elongation at break: JIS K 7113

Notched Charpy impact strength: JIS K 7111

Vicat softening point test: JIS K 7206

Water resistance test: A test piece was immersed in hot water (95° C.),followed by evaluated in accordance with JIS K 7113 (tensile test).Water resistance values shown in Table 1 are relative values, asdetermined when immersion time in hot water required for loweringtensile elongation at break of the test piece of Comparative Example 2to 50% is 100%.

[Materials Employed]

<Polyester Elastomer (A)>

A-1: Polybutylene terephthalate-polycaprolactone block copolymer(product of Toyobo Co., Ltd., polybutylene terephthalate component (60wt. %) serving as a hard segment, number average molecular weight of70,000 determined through the aforementioned GPC)

<Epoxy Compound (B)>

B-1: Alicyclic epoxy compound (product of Daicel Chemical Industries,Ltd., 3,4-epoxycyclohexylmethyl (3,4-epoxycyclohexanecarboxylate), tradename “CELLOXIDE 2021P”, epoxy equivalent: 128 to 145)

B-2: Glycidyl ester compound (product of Mitsui Chemicals, Inc.,diglycidyl hexahydrophthalate, trade name “Epomik R540”, epoxyequivalent: 151 to 172)

<Polycarbodiimide Compound (C)>

C-1: Polycarbodiimide compound derived fromα,α,α′,α′-tetramethyl-m-xylylene diisocyanate (product of NisshinboIndustries, Inc., tradename “Carbodilite V-05”, carbodiimido groupcontent: 5 wt. %, number average molecular weight of 1,000)

<Comparative Polycarbodiimide Compound (D)>

D-1: Polycarbodiimide compound derived from hydrogenated methylenediphenyl-4,4′-diisocyanate (product of Nisshinbo Industries, Inc., tradename “Carbodilite HMV-8CA”, carbodiimido group content: 8 wt. %, numberaverage molecular weight of 2,000).

Examples 1 to 3

In each Example, a polyester elastomer (A), an epoxy compound (B), and apolycarbodiimide compound (C) were mixed at proportions shown in Table 1(unit: parts by weight). The mixture was melt-kneaded and extruded at250° C. by use of a biaxial extruder (30 mmφ). Extruded strands werecooled in a water tank, and the strands were cut by use of a pelletizer,thereby yielding pellets of each polyester elastomer composition. Thepellets were dried at 120° C. for five hours under nitrogen flow.

The above pellets were injection molded at 260° C. by use of aninjection molding machine, thereby producing tensile test pieces andCharpy impact test pieces.

The evaluation results are shown in Table 1. The test results indicatethat, through addition of an epoxy compound and a specific carbodiimidecompound to a polyester elastomer, water resistance is enhanced whilemechanical characteristics are maintained. Thus, hydrolysis resistanceis improved.

Comparative Example 1

The procedure of Example 1 was repeated, except that the proportions ofthe components were changed to the values shown in Table 1. The resultsare also shown in Table 1. As compared with Example 1, water resistanceis poor due to absence of epoxy compound. Thus, hydrolysis resistance ispoor.

Comparative Example 2

The procedure of Example 1 was repeated, except that the proportions ofthe components were changed to the values shown in Table 1. The resultsare also shown in Table 1. As is clear from Table 1, water resistance ispoor when only epoxy compound is added to the polyester elastomer.

Comparative Example 3

The procedure of Example 1 was repeated, except that the proportions ofthe components were changed to the values shown in Table 1. The resultsare also shown in Table 1. As is clear from Table 1, water resistance isconsiderably poor when the added polycarbodiimide compound is differentfrom that of Example 1. TABLE 1 (unit of amount: parts by weight)Comparative Examples Examples 1 2 3 1 2 3 Polyester A-1 100 100 100 100100 100 Epoxy compound B-1 0.4 B-2 0.2 0.2 0.2 0.4 0.2 PolycarbodiimideC-1 0.8 1.2 2 0.8 D-1 0.8 50% Modulus MPa 16 16 15 16 15 15 Tensilestrength at MPa 27 27 25 25 24 25 break Tensile elongation % 500 510 510510 500 500 at break Charpy impact kJ/m² NB NB NB NB NB NB strength(notched) Vicat softening ° C. 170 170 171 170 170 171 temperature Waterresistance % 160 180 200 140 100 140

INDUSTRIAL APPLICABILITY

According to the present invention, a polyester elastomer compositionwhich is excellent in terms of hydrolysis resistance, heat resistance,oil resistance, wear resistance, and impact resistance can be produced.

1. A polyester elastomer composition comprising (A) a polyesterelastomer, (B) an epoxy compound having at least one epoxy group in themolecule thereof, and (C) a polycarbodiimide compound having at leasttwo carbodiimido groups in the molecule thereof, wherein each of twocarbon atoms both adjacent to each carbodiimido group has at least onegroup among (i) an alkyl group having 1 to 4 carbon atom(s) and (ii) asubstituent exhibiting an electronic effect of lowering reaction rate,and wherein the amounts of the epoxy compound (B) and thepolycarbodiimide compound (C) are 0.01 to 10 parts by weight and 0.01 to10 parts by weight, respectively, relative to 100 parts by weight of thepolyester elastomer (A).
 2. A polyester elastomer composition accordingto claim 1, wherein the polyester elastomer (A) contains a crystallinearomatic polyester as a hard segment and at least one species selectedfrom the group consisting of an aliphatic polyester, an aliphaticpolyether, and an aliphatic polycarbonate as a soft segment.
 3. Apolyester elastomer composition according to claim 2, wherein thealiphatic polyester as the soft segment comprises a polycarprolactonecomponent.
 4. A polyester elastomer composition according to claim 1,wherein the polycarbodiimide compound (C) is a compound represented bythe following formula:

wherein R represents a hydrogen atom, an alkyl group having 1 to 4carbon atom(s), or a substituent exhibiting an electronic effect oflowering reaction rate; two Rs linking to a certain carbon atom may bethe same or different from each other, provided that the two Rs are notcoincidentally hydrogen atoms; n is an integer of not less than 2.